"He did have a secret clearance. And he did have a CAC (common access card)," said Thomas Hoshko, CEO of "The Experts," which was helping service the Navy, Marine Corps intranet as a subcontractor for a Hewlett-Packard Enterprise Services contract.

Asked when he was supposed to start work, Mr Hoshko said: "That's what I got to find out, if he was supposed to start today... It's not clear to me."

01.35 (20.35) Navy Admiral Bill French has just spoken at a press conference. He said a total of 14 people have been injured. He would not give details on the types of injuries they sustained. About two thousand people were still within in the facility and evacuation will take another two or three hours.

“Our hearts, our thoughts, and prayers goes out to everyone impacted," he said.

00.41 (19.41) I spent some time earlier with staff, both military and civilian, from the Navy Sea Systems Command as they waited for news of their colleagues. There was a feeling of helplessness that all we could do was gather around the TV to try to piece together what was happening.

-

00.40 (19.40) Obama has called the new director of the FBI, James Comey, to thank him for the bureau's swift response to today's massacre.

Today the President called FBI Director James Comey to express his gratitude for the quick response of Bureau personnel to this morning’s tragic shooting at the Washington Navy Yard. The President also received an update on the ongoing investigation, being led by the FBI. The President commended the FBI and all of the federal agencies involved for their close coordination with the local officials during the ongoing response.

00.35 (19.35) Flags will hang at half mast at federal buildings and at US embassies around the world until sundown on September 20, the White House has ordered.

00.20 (19.20) FBI investigators have concluded that Alexis acted alone and that there was no second shooter, CNN reports.

<noframe>Twitter: Kevin Bohn - Just in: <a href="http://www.twitter.com/evanperez" target="_blank">@evanperez</a> reports FBI has determined there was only one shooter</noframe>

00.15 (19.15) Alexis was reportedly armed with an AR-15, the same weapon used at Newtown and at the Aurora cinema massacre. My colleague Jon Swaine, did a fantastic profile of the gun sometimes called the 'Automatic for the people'.

00.10 (19.10) A man is arrested outside the White House for throwing firecrackers over the fence.

00.07 (19.07) Peter Foster and I have put together a profile of what we know about Aaron Alexis so far. Here's the full report but these are the top lines.

The gunman who killed 12 people in the Washington Navy Yard rampage was arrested on two separate occasions for rage-fuelled incidents in which he apparently fired his weapon in anger – but escaped jail on both occasions.

Hours after the shooting a picture was emerging of Aaron Alexis, 34, as a conflicted young man who was a former Navy Reservist.

Alexis was passionate about Thai culture, attended a local temple in Texas and – according to his father – had been involved in rescue attempts during the September 11 attacks.

In 2004 Alexis was arrested in Seattle after shooting out a man's tires in what he described as a rage-fueled "blackout".

And in 2010 Alexis was arrested in Fort Worth, Texas for firing a pistol through his ceiling to silence an allegedly noisy neighbour, it emerged last night.

Following the Seattle arrest, Alexis' father also told police his son "had been an active participant in rescue attempts on September 11, 2001," according to a Seattle police report.

23.58 (18.58) Fox News is unable to contain its contempt for the person who just set off a security alert at the White House by throwing firecrackers over the fence.

<noframe>Twitter: FOX 5 DC - Reports of shots fired on PA Ave - outside White House - were actually fireworks set off by a likely idiot. Idiot is in custody.</noframe>

23.45 (18.45) When speak at the White House earlier, President Obama described angrily how America had suffered "yet another mass shooting".

By my count this is the sixth time he has addressed a nation rocked by random gun violence: Fort Hood; the shooting of Gabby Giffords in Tucson, Arizona; the massacre in the Aurora, Colorado cinema; the Sikh temple in Wisconsin; the Sandy Hook massacre that killed 20 children; and today.

Compare the photograph of Obama being told about Newtown by his then security advisor Tom Donilon

and the miserably similar picture of him being briefed on today's killing by Lisa Monaco, his counter-terrorism advisor.

-

23.40 (18.40) Here's the original arrest report from the 2004 Seattle incident. The charges were dimissed and Alexis escaped prison, just as he would six years later after firing a bullet through his ceiling into a neighbour's apartment.

23.00 According to a very detailed Seattle Police Dept report, Alexis was previously arrested in 2004 for shooting out the tires of another man’s vehicle in what Alexis later described to detectives as an anger-fueled “blackout.”

He is reported as pulling a gun on construction workers in Beacon Hill, where he was living at the time, and fire three shots into the two rear tires of their Honda before he walked slowly back to his home north of the construction site.

Following his arrest, Alexis told detectives he perceived he had been “mocked” by the workers the morning of the incident and said they had “disrespected him.” Alexis also claimed he had an anger-fueled “blackout,” and could not remember firing his gun at the victims’ vehicle until an hour after the incident.

Alexis also told police he was present during “the tragic events of September 11, 2001″ and described “how those events had disturbed him.”

Detectives later spoke with Alexis’ father, who lived in New York at the time, who told police Alexis had anger management problems associated with PTSD, and that Alexis had been an active participant in rescue attempts on September 11th, 2001.

Armed ATF agents at the scene of the Washington Navy Yard shooting

22.43 David Lawler, in the Telegraph's Washington office, said White House and Capitol building flags will fly their flags at half-mast until Friday.

22.35 Alexis, the suspected shooter, received a general discharge from the Navy Reserve in 2011 after a series of misconduct issues, a Navy official said.

22.30 According to US Navy officials, Alexis won two awards: a National Defense Service Medal and a Global War on Terrorism Service Medal.

22.25 Tiki Confer, the owner of the Bangkok House restaurant in Fort Worth, Texas, said that Alexis was fascinated by Thai culture and would spend hours in her restaurant practicing the language.

"He was very interested in all Thai things. He was really nice and wanted to speak Thai and actually learned pretty fast," Ms Confer, who is known locally as "Mama Tiki", told The Daily Telegraph.

Alexis spent a long time visiting with monks at a nearby Buddhist temple but Ms Confer said she had not seem since 2008. "He seemed to be a very happy guy, always smiling," she said.

A picture from earlier shows Navy Yard workers with their hands above their head as police search the premises

22.23 Reached by telephone, Aaron Alexis' father, Algernon Alexis, seemed stunned by the news his son may have been involved.

"This comes as a complete shock," he said and then asked a Reuters reporter how he could reach authorities leading the investigation. He said his son was former military and now studying while working in a computer-related job for a private company.

22.17 Today's attack is the ninth deadliest shooting in recent US history, a list the country has had to update several times in the last few years. The Virginia Tech massacre claimed the most lives with 32 killed, while 26 children were shot dead at Sandy Hook elementary school last year.

22.04 DC police chief has spoken of "multiple engagements" between police and suspect at the Navy Yard, ending with "final gun battle" in which Alexis died.

21.52 The FBI's description of Alexis:

Date(s) of Birth Used: May 9, 1979

Place of Birth: Queens, New York

Height: 6'1"

Weight: 190 pounds

Hair: Black

Eyes: Brown

Sex: Male

Race: Black

21.48 To confirm, the death toll has risen to 13. Janis Orlowski, chief operating officer of Washington Hospital Center, said the hospital was treating three gunshot victims in critical condition. One was a Washington police officer and two were civilian women.

Orlowski said the police officer had gunshot wounds to the legs. One woman had a gunshot wound to the shoulder, and the other had gunshot wounds to the head and hand.

21.42 A picture of Aaron Alexis, the suspected gunman, has been posted on the FBI's website, where the appeal for any information on him.

We have some of our own. According to the Washington Post, Alexis achieved his final rank of Aviation Electrician’s Mate 3rd Class in December 2009. Officials said they did not immediately know the reasons for his discharge.

Alexis was assigned to the Fleet Logistics Support Squadron 46 at Naval Air Station Fort Worth in Texas for the bulk of his time in the military, from 2008 until he left the service in 2011, records show. He was awarded the Global War on Terrorism Service Medal and the National Defense Service Medal— two common awards for military personnel

21.35 Our US correspondent Nick Allen says the officers who rushed to the shooting include a team of elite agents who were instrumental in capturing alleged Boston Marathon bomber Dzhokhar Tsarnaev.

The team, which is based in Washington, consists of a cadre of officers who are trained for "high-risk operations" including manhunts, hostage rescue and "dynamic entry techniques," and was called in as local policie feared they may have two gunmen on the run.

Read more on this here.

21.18 It has been reported by news agencies that Aaron Alexis served in the Navy reserves from May 2007 to January 2011.

21.15 A police officer and two civilians are being treated in hospital and are expected to recover.

21.11 AP is reporting that Aaron Alexis, the suspect gunman, is believed to have gotten into the Navy Yard by using someone else's identification card. It is not yet clear if that person was an accomplice or if the ID was stolen.

21.01 The Senate is now in lockdown and will be in recess until tomorrow. Senate officials took the decision to seal the building amid ongoing uncertainty about the possibility that another gunman may still be at large.

20.53 The Washington Nationals baseball team have said they are postponing tonight's game against the Atlanta Braves as a mark of respect. Nationals Park is only a few streets from the Navy Yard.

Emergency responders arrive at the scene of a shooting at the Washington Navy Yard

20.47 We have this from Raf Sanchez, our correspondent on the scene:

I've been with military and civilian personnel from the Navy Sea Systems command in an office building a few blocks from the scene of the shooting. Some of them saw the gunman on the third floor of building 197 and are waiting to be interviewed by the FBI. Others simply have nowhere to go for now while they try to figure out how they are going to make it home without their cars, which are still inside the locked-down police cordon.

The mood is understandably sombre and the staff here expect to know at least someone, or perhaps several people, who were killed in the rampage. "It's just going to be so hard when the names start coming out," said one staff member, who asked not to be identified. For now they continue to gather around the television, watching images of their office building surrounded by heavily-armed police, grateful to be alive but bracing for bad news to come.

20.43 The suspect killed by police at the Navy base has been named by officials speaking to Reuters and AP news agencies as Aaron Alexis, 34, formerly of Ford Worth, Texas.

20.33 The Washington Post are reporting it is the worst single loss of life within the District of Columbia since an airliner plunged into the Potomac River in 1982, killing 78.

20.16 Nick Allen, US correspondent, writes that officers who rushed to reponde to the shooting included a team of elite agents instrumental in capturing alleged Boston Marathon bomber Dzhokhar Tsarnaev.

Twenty special agents from the US Bureau of Alcohol, Tobacco, Firearms and Explosives were dispatched to the scene, including the Special Response Team that helped track Tsarnaev in Boston.

The team, which is based in Washington, consists of a cadre of officers who are trained for “high-risk operations” including manhunts, hostage rescue and “dynamic entry techniques,” and was called in as local policie feared they may have two gunmen on the run.

The Washington-based team is one of five regional ones that the ATF has baseded across the country. The teams have been deployed 217 times over the last five years.

In April the Washington team went to Boston and was involved in the manhunt for Tsaranev, which ended with him being tracked to a boat where he was hiding in a suburban garden.

A police officer pauses after leaving the scene of a shooting at the Navy Yard in Washington

20.11 As police continued to search for one other possible gunman, the US Senate, which less than two miles from the Navy Yard, announced it would be locked down "out of an abundance of caution" for the safety of staff and legislators.

Workers of the US Capitol in general are being told to stay indoors.

20.00 Washington DC police have rule out one of the two "suspects" - so that means there is only one suspect they want to talk to.

<noframe>Twitter: DC Police Department - The white male in the tan outfit has been identified and is not a suspect or person of interest.</noframe>

19.33: The Associated Press is reporting that the gunman has been identified as a Navy employee whose work status had been changed earlier this year, citing a federal government official speaking anonymously.

While that may suggest the motive was job related, authorities haven't ruled out anything including terrorism, the official said.

NBC's Pete Williams claims that he is a 34-year-old from Texas.

19.29 NBC, who earlier put out the wrong name of the potential suspect, has reported that police found an ID beside the suspect. They are now interviewing that person to find out why his ID was found.

Pete Williams is also reporting that they have a potential name of a suspect, which is being vetted as we speak.

<noframe>Twitter: Chuck Todd - .<a href="http://www.twitter.com/PeteWilliamsNBC" target="_blank">@PeteWilliamsNBC</a> also reporting that law enforcement has a potential name of the suspect; being vetted now to triple check, obviously</noframe>

19.27 Devlin Barrett of the Wall Street Journal has summed up an issue with breaking, crime reporting:

19.12 She says they have multiple bits of information that point to two men who were carrying firearms and she believes they were involved in some way and they are trying to locate them.

She says the search could take another couple of hours.

19.10Chief Cathy Lanier of DC police is back.

She has confirmed 12 dead. There are a few additional people who were injured, including officers - only one by gunfire.

More on suspects - a white male between 40-50, wearing a tan military uniform consistent with naval uniform, and a black male between 40-50 in camouflage, approximately 5ft 10.

She says a large part of the area is still in lockdown, and there is an additional search for the extra suspects.

The motive for the shooting is unknown.

I just want to start off by saying as far as the initial response this morning, you’ve heard that we have at least one officer with gunshot wounds that is currently being treated, but the response by uniformed police officers… was absolutely nothing short of heroic. With at least 12 confirmed dead at this point, I think the actions by the police officers without question helped to reduce the number of lives lost. So our hearts go out to the families, certainly of all the victims here, but our gratitude to the front line officers… who ran into danger this morning.

18.52 Jay Carney, the White House press secretary, has echoed Barack Obama's sentiments that his thoughts are with the victims. When pressed about the Obama adminsitration's views on gun control, he refuses to comment.

<noframe>Twitter: David Nakamura - Carney won't say if WH will use Navy Yard shooting to renew push for gun control legislation, saying it is an "ongoing investigation"</noframe>

18.40 Alexei Pushkov, the chairman of the Russian Duma’s Foreign Affairs committee, took to Twitter to blame the shootings on “American exceptionalism.”

In a tirade in Russian and English the hawkish MP said the shooting showed the only thing exceptional about Americans was their “animosity.”

“A new shooting at the Washington Navy Yard – one shooter and 7 bodies. No one is surprised anymore. A vivid confirmation of “American exceptionalism” he tweeted in Russian.

Switching to English, he added:

<noframe>Twitter: ÐÐ»ÐµÐºÑÐµÐ¹ Ð&Yuml;ÑÑÐºÐ¾Ð² - The USA should part with the notion of American exceptionalism. It contradicts the principles of equal rights and smells of political racism</noframe>

Then in Russian again: “For prosing the US abandon the notion of American exceptionalism, “democratically” thinking Americans showered me with insults. Read it.”

“The stream of hatred from American citizens is striking. One wrote: ‘apparently we (i.e. the US) saved you for nothing in World War Two’ !!!”

18.32 A US official has told Reuters that a preliminary report shows 12 people were shot at the Navy yard, including seven dead.

18.31 Two workers at the Navy yard who came face to face with the gunmen said he said nothing as he raised his rifle and opened fire on them.

Terrie Durham, a civilian employee in the Office of Naval Sea Systems Command, told NBC news: "We're lucky he was far enough away he was a bad shot."

Navy Commander Tim Jirus said a man was shot right beside him when asking him what was going on.

He just came up and was like, 'Hey I understand you have a shooter in your building...

I said I heard some things earlier, I don't know if they were gun shots. And then I heard two more gunshots and it hit the guy next to me and not me.

It is the Navy's oldest on-shore installation, where 3,000 still work today.

Commanders ordered it burned to the ground during the War of 1812 to prevent the British from capturing it. Robert Fulton did torpedo research there, and Charles Lindbergh went to the yard after his 1927 transatlantic flight. The locks for the Panama Canal were built at the site.

It became a ceremonial and administrative center for the Navy and was transformed into a modern office centre in the 1990s.

It's home to the Chief of Naval Operations and the Naval Historical Center. It also serves as headquarters for Naval District Washington and several other commands. The Navy Museum is open to the public.

18.00Todd Brundidge, an executive assistant at Navy Sea Systems Command, was at his desk shortly after 8am, checking emails and preparing for the day. He's been speaking to Raf Sanchez:

First the fire alarms went off outside his third floor office and moments later a colleague ran past, shouting: "There's a shooter outside, this is for real, this isn't a drill."

Mr Brundidge, 45, ran into an adjacent office to warn colleagues and as they ran out of the office they heard the first wave of shots.

"There was a tall black guy who stepped around the corner maybe 20 yards from us with a gun in his hand. He pointed the gun our way and started shooting," Mr Brundidge told the Daily Telegraph. He said the gunman wore an all-blue outfit and that the weapon appeared to be a handgun. The gunman said nothing as he fired down the hall.

"I feel really lucky because if it had been two or three seconds later he could have been up right up on us. I'm just lucky to be here," he said.

"Everybody was pushing and shoving and screaming 'Oh my god, there's a shooter, there's a shooter,' as they ran down the stairs. We didn't know if the guy was coming down behind us.

Staff found a closed gate as they left the building and some climbed over a seven-foot brick wall as they tried to get away from Building 197.

"You these things on the news every day and you just never know when it's going to happen in your work area. I don't know who the shooters are, you just don't know what's going to make the next person snap," he said.

He and other colleagues waited in a nearby office building, eating biscuits and drinking coffee, as they waited to be interviewed by the FBI.

17.33Barack Obama, who was due to speak on the economy, is speaking about the shooting.

I’ve been briefed by my team on the situation. We still don’t know all the facts. But we do know that several people have been shot, and some have been killed. So we are confronting yet another mass shooting. And today it happened on a military installation in our nation’s capital. It’s a shooting that targeted our military and civilian personnel.

These are men and women who were going to work, going their job protecting all of us. They’re patriots. And they know the dangers of serving abroad, but today they faced the unimaginable violence that they wouldn’t have expected here at home.

So we offer our gratitude to the Navy and local law enforcement, federal authorities and the doctors who’ve responded with skill and bravery. I’ve made it clear to my team that I want the investigation to be seamless so that federal and local authorities are working together. And as this investigation moves forward, we will do everything in our power to make sure whoever carried out this cowardly act is held responsible.

In the meantime, we send our thoughts and prayers to all at the Navy Yard who’ve been touched by this tragedy. We thank them for their service. We stand with the families of those who’ve been harmed. They’re gonna need our love and support.

And as we learn more about the courageous Americans who died today, their lives, their families, their patriotism, we will honor their service to the nation they helped to make great. And obviously, we’re gonna be investigating thoroughly what happened, as we do so many of these shootings, sadly, that have happened, and do everything that we can to try to prevent them.

President Barack Obama comments on the shootings at the Washington Navy Yard

17.24 A Spokesman from George Washington University Hospital has confirmed one fatality. A Male who was shot in the temple and was dead on arrival.

17.15 Chief Cathy Lanier of Metropolitan DC police follows Mr Gray. She says one police officer has been shot after engaging with police.

She confirms that they have ONE shooter who was involved in the incident and he is deceased.

They have other casualties inside.

She says the big concern for the is that they potentially have two additional shooters who are still out there.

17.12 Mayor Vincent Gray of Washington says a gunman entered building 197 and began shooting.

They launched a search for the gunman.

He says they know four have been wounded, taken to hospital. They are trying to confirm the number of fatalities involved.

"As far as we know, this is an isolated incident," he says.

17.10 Raf Sanchez spoke to Captain Michael Graham, a 28 year veteran of the Navy who had received a first hand description of one of the shooters from a colleague. Captain Graham was told that the shooter was a "tall olive-skinned male wearing fatigues, but it did not look like a US military uniform. He was carrying an M-16 like weapon."

Captain Graham also provided details of the security arrangements in building 197. He told Raf that in order to get onto the base employees have to show a pass. Individuals are then able to walk in the front door of building 197 without scanning anything but that will only get them as far as the lobby. To actually get into the heart of the building the individual would have to scan a pass at a guard station.

Captain Graham said very few of the military themselves on the base are armed, those armed are typically security guards and police officers.

17.08 Shootings on US bases are relatively rare. Arguably the most infamous was on November 5, 2009, when Major Nidal Hasan killed 13 people and wounded 32. Here are others from the last 20 years.

January 25, 1993: Gunman opens fire at CIA headquarters in Langley, VA, killing two CIA employees and wounding three others. Mir Amal Kansi is found guilty of capital murder and nine other charges, having been turned over to face trial in November 1997.

July 4, 1997: Members of the splinter militia group the Third Continental Congress are arrested while planning attacks on military bases which they believed were being used to train United Nations troops to attack U.S. citizens.

June 1, 2009: Private William Long was killed, and a second injured in shooting attack at Army Navy Career Centre, Little Rock, Arkansas.

Nov 5, 2009: Nidal Hasan opens fire at Fort Hood, a U.S. Army base in Texas, killing 13 people and wounding 32. An Army major is charged in connection with the rampage. In August he was sentenced to death.

March 4, 2010: Gunman John Patrick Bedell shot and wounded two Pentagon police officers at a security checkpoint in the Pentagon station of the Washington Metro in Arlington County, VA.

March 22, 2013: Two active-duty marines were shot in an incident linked to a "love triangle" at Marine Corps Base Quantico in Northern Virginia. The shooter, Sgt. Eusebio Lopez, died of a self-inflicted gunshot wound.

17.00 Paul Desbiens, a Navy contractor, said he did not hear or see anything until the fire alarm went off about 8.30.

16.57 The US Navy wanted family members who want to know about their loved ones how to get in touch

<noframe>Twitter: U.S. Navy - Family members looking for information about their loved ones can call 202-433-6151 or 202-433-9713. <a href="http://search.twitter.com/search?q=NavyYardShooting" target="_blank">#NavyYardShooting</a></noframe>

16.51Ray Mabus, the US Secretary of the Navy, has said he is shocked by the tragedy this morning. He has released a couple of statements via Twitter:

<noframe>Twitter: SECNAV Ray Mabus - I'm deeply shocked &amp; saddened by the shooting this morning at the Navy Yard. Our thoughts &amp; prayers are with the victims and their families.</noframe>

<noframe>Twitter: SECNAV Ray Mabus - I have complete confidence in our first responders, and I continue to be completely focused on this very difficult situation.</noframe>

16.43 The Associated Press is reporting that a US law enforcement official claims the gunman at the Navy yard has died.

16.42 MedStar hospital is holding a press conference now. They have said they have three patients - a correction from earlier. There is also heightened security around the hospital.

Janet Orlowski, a spokesman, says the victims "have severe injuries", but are conscious, "alert and speaking at this time".

She added that one of those in the hospital is a police officer.

She says they have report of individuals who have died at the scene. She does not know the number of those who have died.

"We are telling authorities that we can take an additional eight to ten individuals here. We are not sure if we will get that many but they have told us that they believe that there will be more victims coming."

16.35 Ed Zeigler, director of public affairs for the Naval District of Washington told MyFoxDC.com that two suspects were "down" as a result of gunfire

16.34 Col Bill Cowan, a former Marine commander, tells Sky News that he has heard reports that a gunman had taken shots from a window.

16.28 Annamarie DeCarlo, a spokesman for MedStar Washington Hospital Centre, has told The Washington Post that the hospital has two patients from the shooting that are being treated in their trauma unit.

16.25 A US defence official has told the AFP news agency that a gunman has shot and killed more than one person.

16.18 Sky News is now reporting that two suspects have been "taken down". If it is two gunmen then, it raises the possibility that this is more than a disgruntled lone gunman. We should get an update in about 10 minutes.

16.17 Washington Police Department has information for family members:

16.15 Chuck Hagel, the US defence secretary, is receiving regular updates on the shooting.

"We believe there has been loss of life and several injuries," Pentagon press secretary George Little said. He said he could provide no additional details and could not confirm the number of fatalities or injuries, saying the "situation remains fluid."

16.14 We've got some video from Now This News of emergency crews arriving at the scene.

16.12 A note on security from Raf: Before 6.30am you need to scan your pass to open the door at Building 197, after that there's no key card. Employees do not have to go through metal detector to get in.

16.05 Raf Sanchez has just spoken to Patricia Ward, a civilian logistics manager at the Navy yard. She has worked for the US government for 37 years and said she was frightened to go into a government building now.

She was paying for breakfast on the 1st floor of building 197 when the shots rang out.

I just paid for my breakfast when I heard 'POP POP POP' and every started running. There was at least 3 more shots - I think I heard seven in total. We all just looked at each other and started running. That's when I saw a female security guard with her gun drawn and she told everybody to get out of the building.

I'm scared and I'm nervous and I don't feel secure coming into government buildings.

15.58 A law enforcement officer aims his rifle to a building as he responds to the shooting.

15.53 The latest from the Washington Post appears to suggest that police believe two shooters were involved in the incident, evoking memories of the Boston Marathon Bombing earlier this year when brothers Tamerlan and Dzhokhar Tsarnaev killing three people and injured dozens. I must stress though that the two gunmen has not yet been confirmed.

Law enforcement officials stand together at the Washington Navy Yard

15.50 The Navy said "several" people were killed at the Navy Yard according to USA Today. Ed Buclatin, the public affairs chief for the Navy Installations Command, tweeted "four killed and eight injured." He also tweeted that reports of more than one shooter had not been confirmed.

15.45 Two Navy Yard employees, Terri Durham and Todd Brundage, have been speaking to CNN after escaping as the gunman opened fire.

“At first we thought there was fire emergency in the building but our fire wardens came running very quickly yelling for everyone to get out of the building and that’s when we started running.

Asked what kind of gun it was, Miss Durham added: “it appeared to be a rifle, or that’s the best we could tell from that distance. We saw him hold the rifle, and aim it and raise in our direction.

Todd Brundage added: “Just get out of the building as quick as you can. People were pushing and shoving and falling down. As we came outside people were climbing the wall, trying to get out. It was just crazy.”

“He was a tall black guy, he didn’t say a word. He just look at us for two or three seconds. I got a look at the guy and as we starting going out the door he turned and he started shooting and we immediately made a left to get down the stairs and get out to the building. “

15.42 Washington DC police is working a press briefing. We will bring it to you as it happens.

15.38 The latest statement from the Navy says for the first time there are reports of fatalities.

Several people were injured and there are reports of fatalities in a shooting at the Washington Navy Yard Sept. 16.

I got a call from my cousin who's in New York telling me that there was a shooting at the building my aunt was at. 'Mommy's in the building, there's been a shooting at mommy's building.'

Mr Kier said he had texted his aunt but had no response. "This has blown my mind, I'm trying to hold it together," he said.

His 76-year-old mother lives nearby and Mr Kier said the family was deliberately not telling her that her only sister was at the scene of the shooting.

"I'm sure she's wondering what's going on down here. I'm not sure she really understands there's a possibility her sister is caught up in this. Somebody is going to get very bad news today," he said.

15.28 For those of you that don't know the area, here is where the Navy yard is located:

15.24 The Washington Post now says that there are reports police are searching for three shooters - including at least one in army fatigues.

Police said at least one of the shooters is “down,” but it was unclear whether that means the suspect has been arrested or shot. Two remain at large, and police believe they have pinned down one between the third and fourth floors of one of the buildings on the installation in Southeast Washington.

15.23 A senior Naval Officer at the ship yard has told NBC that 12 people have been shot, with four of them believed dead. This has not yet been confirmed.

A police helicopter hovers over the scene as armed response units check the roof of one of the buildings in the Washington Navy yard

15.11 A White House official has released a statement on the shooting:

The President has been briefed several times about the unfolding situation at the Washington Navy Yard by Assistant to the President for Homeland Security and Counterterrorism Lisa Monaco and Deputy Chief of Staff Alyssa Mastromanaco. The President directed his team to stay in touch with our federal partners, including the Navy and FBI, as well as the local officials. We urge citizens to listen to the authorities and follow directions from the first responders on site.

15.08 Raf Sanchez has just spoken to someone's brother inside.

He is at the corner of M and 3rd street which is about two blocks from the Navy yard which is as close as they're allowing us.

I've just spoken to Damiene Johnson, 21, whose brother is a contractor with the Navy and was inside Building 197 when the shots rang out.

His brother is currently in his car inside the Navy yard and is not being allowed to leave.

Mr Johnson said: "He [his brother] heard multiple shots ring out and as soon as he peaked his head around the corner all he saw was everybody running and then was told to evacuate the building."

15.00 We have a description of the shooter, via Washington's Metropolitan Police Department.

14.51Washington Metropolitan Police has confirmed that five people have been injured in the shooting, according to Sky News.

14.43 The Washington Post is reporting that a lone gunman has barricaded himself in after allegedly shooting at least three people.

Police and emergency services on M Street by the Washington Navy Yard

Police tape off the area following reports of a shooting at the Washington Navy Yard

14.37 Twitter user Bill Raines is tweeting from the scene, and has posted a picture that appears to show of a victim receiving CPR on the street.

Police respond to the report of a shooting at the Navy Yard in Washington. (SAUL LOEB/AFP)

14.28 A police spokesperson has confirmed that the shooter is still 'active' and that initial reports suggest that the suspect is male, but no more details. About 3,000 people work at the headquarters, according to the Navy, which is responsible for building and buying US warships and combat systems, the navy said.

14.25 Acccording to the Washington Post, police have said there are three, possibly four, victims. Police have not commented on the status of the victims.

14.22 Media footage shows a police helicopter in circling very low over the scene.

14.18 Police on the scene have said two people have been injured, but have refused to comment on the status of the victims. Unconfirmed reports suggest that a police officer may have been injured, and that a suspect in on the loose with an assault rifle.

14.00 UK (09.00 US) A shooter has opened fire at a US Navy base in Washington, according to police and the FBI. The US Navy has said on Twitter that the suspect is still on the loose and that approximately 3000 people work in the building.

The Washington Navy Yard says on its website that it's the Navy's oldest shore establishment. It is home to the chief of Naval Operations and is headquarters for numerous naval commands.